Method for manufacturing resin shaft member, mold, and roller shaft

ABSTRACT

A mold used to mold a resin roller shaft including a shaft portion and a roller joint portion configured to join a roller includes a plurality of cavities of different shapes for molding a roller joint portion. At least one of the plurality of cavities includes a space portion surrounded by a parting-free surface formed by an insert. The insert is larger in inner diameter than the shaft portion, and is movable by an ejector in the opening/closing direction of the mold.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a manufacturing method for manufacturing a resin shaft member by injecting a resin material into a mold, a molding mold, and a roller shaft.

2. Description of the Related Art

Conventionally, a roller shaft used to convey paper in a copying machine or printer is manufactured by press-fitting and joining a rubber roller on a metal shaft. At a portion of the shaft at which the requested rigidity is low, a resin shaft is used.

A shape such as a key groove is added to a metal shaft by processing part of the end face later. As a rust prevention measure for a post-processed portion, plating is performed.

A resin shaft needs to have a rib structure because it is difficult to manufacture a columnar round shaft, in order to ensure the shaft accuracy and prevent a sink mark or the like. When rubber is press-fitted and joined to the rib portion, the outer shape accuracy of the rubber degrades and the surface needs to be polished.

Further, a mold for molding a shaft has a parting between the stationary side and the movable side. Even a step or a small flash at the parting line affects the accuracy of the rubber surface after press-fitting the rubber.

As a method of forming a resin shaft into a columnar shape, there is proposed a method of filling the inside of a mold with a gas to form a hollow structure when filling the inside of the mold with a resin (see Japanese Patent Application Laid-Open No. H08-132467).

As a method of removing a parting line on the end face, there is proposed a method of arranging a piece on the end face in a direction perpendicular to the mold opening/closing direction (see Japanese Patent Application Laid-Open No. 2001-18226).

Further, there is proposed a method of forming a shape such as a gear on the end face (see Japanese Patent Application Laid-Open No. H10-281139).

SUMMARY OF THE INVENTION

A conventional method has problems in the weight of a finished piece and the manufacturing cost of a roller shaft because the weight of a metal shaft is heavy, the end portion requires fabrication, and the surface needs to undergo rust prevention plating.

A resin shaft needs to have a rib structure because it is difficult to manufacture a columnar round shaft, in order to ensure the shaft accuracy and prevent a sink mark or the like. When rubber is press-fitted and joined to the rib portion, the outer shape accuracy of the rubber degrades and the surface needs to be polished.

Further, a mold for molding a shaft has a parting between the stationary side and the movable side. Even a step or a small flash at the parting line affects the accuracy of the rubber surface after press-fitting the rubber.

According to the present invention, there is provided a mold used to mold a resin shaft member including a shaft portion and a roller joint portion configured to join a roller, comprising a plurality of cavities of different shapes, wherein at least one of the plurality of cavities includes an insert having a space portion which is surrounded by a parting-free surface and used to mold the roller joint portion, and a gate configured to inject a resin into the space portion, the space portion is larger in diameter than the shaft portion, and the insert is movable by an ejector in an opening/closing direction of the mold.

According to the present invention, there is provided a method of manufacturing a resin shaft member including a shaft portion and a roller joint portion configured to join a roller, comprising: molding, by using a mold including at least a first cavity and a second cavity, a first part on which the shaft portion is molded by the first cavity, and molding a second part on which the roller joint portion is molded on the first part by the second cavity in which the first part is inserted.

According to the present invention, there is provided a roller shaft which is obtained by joining rollers to a plurality of roller joint portions of a resin shaft member on which a shaft portion and the plurality of roller joint portions are integrally molded, wherein the roller joint portion has a seamless shape.

A shaft member with a large shaft diameter requiring high shaft rigidity is molded using a foaming resin material, thereby molding a high-accuracy cylindrical resin shaft member free from any sink mark.

In a mold for molding a resin shaft member according to the present invention, a plurality of parting-free inserts is arranged at portions to each of which a roller is press-fitted and joined. In addition, a plurality of cavities are arranged in accordance with the number of roller joints.

When molding a resin shaft member according to the present invention, a molded article molded by the first cavity is inserted in the second cavity to mold a rubber roller joint portion. Sequentially, the next roller joint portion is molded by the third cavity.

In the present invention, a plurality of parting-free inserts were arranged in the mold in accordance with the number of roller joint portions, and roller joint portions were sequentially molded in the mold. Thus, the roller joint portions for press-fitting and joining a roller could have a parting-free seamless shape.

As a result, in the present invention, the roller surface accuracy upon press-fitting and joining a rubber roller at a roller joint portion became high, and conventional roller surface polishing could be omitted.

A shaft requiring high rigidity was molded by the mold and molding method according to the present invention using a foamed material as the resin material. Hence, a cylindrical shaft member with high rigidity and high accuracy of a roller joint portion without any sink mark could be manufactured, and a metal shaft could be replaced with a resin shaft.

Therefore, a resin shaft member according to the present invention could have high accuracy and high functionality at low cost, and could improve the productivity and quality.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a shaft member according to an embodiment of the present invention.

FIG. 2 is a sectional view of the shaft member in the shaft direction according to the embodiment of the present invention.

FIG. 3 is a sectional view of a mold according to the embodiment of the present invention.

FIG. 4 is a sectional view showing a state in which the mold is open according to the embodiment of the present invention.

FIG. 5A is a front view of the movable side of the mold according to the embodiment of the present invention when viewed from a direction in which the mold is opened/closed, and showing a state in which molding operations are performed simultaneously in respective cavities.

FIG. 5B is a front view of the movable side of the mold according to the embodiment of the present invention when viewed from the direction in which the mold is opened/closed, and showing a state in which the mold is opened to extract molded articles from the respective cavities.

FIG. 5C is a front view of the movable side of the mold according to the embodiment of the present invention when viewed from the direction in which the mold is opened/closed, and showing a state in which the respective molded articles are extracted rightward in FIG. 5C after the time further elapsed from the state in FIG. 5B.

FIG. 6A is a perspective view showing a mold according to another embodiment of the present invention, and showing a state in which the molding operation of the mold is being performed.

FIG. 6B is a perspective view showing the mold according to the other embodiment of the present invention, and showing a state in which the mold is opened to eject an ejector after molding.

FIG. 6C is a perspective view showing the mold according to the other embodiment of the present invention, and showing a state in which the molded articles of shaft members molded by respective cavities are released from the mold.

FIG. 6D is a perspective view showing the mold according to the other embodiment of the present invention, and showing a state in which the molded articles molded in FIG. 6C are inserted again in the mold.

FIG. 6E is a perspective view showing the mold according to the other embodiment of the present invention, and showing a state in which the insertion of the molded articles is completed, and the inserted molded articles, slides, and inserts move together with backward movement of an ejector plate.

FIG. 7 is a perspective view showing a state in which molded articles are inserted in cavities.

FIG. 8 is a perspective view showing another molded article of a shaft member molded by a mold and molding method according to each embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings. The same reference numerals denote the same parts throughout the drawings.

FIG. 1 shows a resin shaft member according to an embodiment of the present invention. A shaft member 10 includes a cylindrical shaft portion 1, a plurality of roller joint portions 2 which are larger in outer diameter than the shaft portion 1 and to which rubber rollers are joined, and a key groove 3 formed on at least one end of the shaft portion 1. A parting line 4 is formed on the shaft portion 1. The roller joint portions 2 are arranged equally in the shaft direction. The roller joint portions 2 do not have a parting line.

FIG. 2 is a sectional view of the resin shaft member according to the embodiment of the present invention. The shaft portion 1 includes a roller joint portion 6 which is integrally molded with the shaft portion 1. The shaft member 10 (shaft portion and roller joint portions) incorporates a foam layer 5. The foam layer 5 inside the shaft portion 1 is formed continuously in the shaft direction of the shaft portion 1.

To the contrary, roller joint portions 7 are molded and integrated with the shaft portion 1 after molding the shaft member 10. A non-foam layer 8 molded using a non-foaming resin is formed at the boundary between each roller joint portion 7 and the shaft portion 1.

The roller joint portion 7 has a parting-free seamless shape.

A roller is press-fitted and joined at the roller joint portion, forming a roller shaft. Since the roller joint portion has a parting-free seamless shape, the roller surface accuracy upon press-fitting and joining a roller at the roller joint portion 2 is high, and conventional roller surface polishing can be omitted. The roller preferably uses, e.g., rubber, but a roller made of a substance other than rubber is also available.

The shaft member 10 can use a resin material such as high-impact polystyrene (HIPS), acrylonitrile butadiene styrene (ABS), polycarbonate (PC), modified polyphenylene ether (PRO), polystyrene (PS), polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), a liquid crystal polymer (LCP), or polyacetal (POM).

It is also possible to increase the strengths of the shaft portion and shaft member 10 by filling one of a glass filler, carbon fiber, talc, and plate-like filler in the resin material at the shaft portion 1. A combination of these fillers can also be used.

By manufacturing the shaft member 10 according to the present invention by using a foaming resin, as shown in FIG. 2, a cylindrical shaft member with high rigidity and high accuracy of a roller joint portion without any sink mark can be manufactured. In particular, the present invention is effectively applied to a shaft member with a large shaft diameter requiring high shaft rigidity.

Since a sink mark and warping, which appear in a thick shaft member, change depending on the maximum diameter of the shaft member and the molding cycle, the resin material is not always limited to a foaming resin material. A non-foaming resin is also usable in accordance with a desired shape or the type of resin material.

FIG. 3 is a sectional view of a mold used to mold the shaft member according to the embodiment of the present invention. A mold 40 has a plurality of cavities of different shapes.

At least one of the plurality of cavities, at a portion thereof, includes a space portion (shape serving as a roller joint portion) which is surrounded by a parting-free surface formed by an insert 9. And the insert 9 is used to mold a roller joint portion. Further, the mold 40 includes gate 41 for injecting a resin into the space portion of the insert 9, a runner 11 to which a resin material is supplied from the outside, ejector rod 12, and an ejector plate 13. The diameter of the space portion of the insert 9 is larger than the inner diameter of the shaft portion 1. The insert 9 does not have a parting, so no parting line is generated on a roller joint portion molded by the insert 9.

One of the plurality of cavities is a cavity for molding a shaft portion, and has a gate for injecting a resin into the shaft portion.

In FIG. 3, a resin material supplied from a supply source (not shown) passes through the runner 11 and gate 41 to fill the inserts 9 of the cavity for molding a shaft member and the cavities for molding a roller joint portion.

After a dwell step and cooling step upon filling the resin material, the mold 40 is opened, and the ejector plate 13 and the ejector rod 12 coupled to the ejector plate 13 are pushed out to move the insert 9 coupled to the ejector rod 12 in the die opening/closing direction.

Although the molded article (part) of a shaft member is temporarily extracted from each cavity, a molded article (part) which has not had a final shape yet is inserted again into the mold 40.

After inserting the molded article (part) which has not had a final shape yet, the roller joint portion 6 is molded again, as needed. A molded article (part) on which molding of the necessary roller joint portions 6 has ended is extracted as a final molded article (resin shaft member) without returning it to the mold 40.

FIG. 4 is a sectional view showing a state in which the mold 40 is open.

In FIG. 4, inserts 91 to 93 each having the shape of the roller joint portion 6 move in the mold opening/closing direction from the mold 40 by an ejector together with resin reservoirs 14 of the gates, and are exposed.

When the mold 40 is opened to push out the ejector plate 13, as shown in FIG. 4, the inserts 91 to 93 each having the shape of the roller joint portion 6 also move so that molded articles (parts) can be moved and released in a direction perpendicular to the mold opening/closing direction.

FIGS. 5A to 5C are front views of the movable side of the mold according to the present invention when viewed from a direction in which the mold 40 is opened/closed. A first part 15 molded by the first cavity, and a second part 16 molded by the second cavity are arranged from the top of the mold 40.

Holding portions (for supporting a part serving as a molded article) are formed at the two end portions of each cavity to support the shaft center of a shaft portion on one end face in the shaft direction. One of the holding portions includes a slide member 18 movable in a direction perpendicular to the mold opening/closing direction, and the other includes a block 19. In molding, the first part 15 and second part 16 serving as molded articles are held at the two ends in the shaft direction in the respective cavities.

In FIG. 5A, molding operations are performed simultaneously in the respective cavities. When the die 40 is opened, the first part 15 molded by a first cavity 101 is extracted and set in a second cavity 102 to mold the second part 16 on which a roller joint portion 23 is molded.

As shown in FIGS. 5A to 5C, the mold may have the third cavity. By the third cavity, a third part 17 is molded.

Similar to the operation of setting the first part 15 in the second cavity 102 to mold the second part 16 on which the roller joint portion 23 is molded, when the mold 40 is opened, the second part 16 on which the roller joint portion 23 is molded by the second cavity 102 is extracted and set in a third cavity 103 to mold the third part 17 on which a roller joint portion 25 is molded. A roller joint portion 22, a roller joint portion 24, and the roller joint portion 25 are molded at different positions.

FIG. 5B shows a state in which the mold 40 according to the present invention is opened to extract molded articles from the respective cavities.

In FIG. 5B, the insert having a roller joint portion, and the block which is arranged for each cavity to support the shaft center of a molded article on the end face move forward along with forward movement of the ejector plate, and the slide 18 moves rightward on the paper surface. After that, molded articles molded by the respective cavities are extracted rightward in FIG. 5B, and temporarily released from the mold 40 by a robot or the like.

FIG. 5C shows a state in which the respective molded articles are extracted rightward in FIG. 5C after the time further elapsed from the state in FIG. 5B. As described above, after molded articles are molded by the respective cavities and temporarily extracted, molded articles except for one molded by the third cavity 103 are inserted again in cavities in the next stages to sequentially mold roller joint portions.

As described above, the parts 10 are simultaneously molded by the respective cavities. After the mold 40 is opened, the molded parts are sequentially inserted in adjacent cavities of different shapes and then the mold 40 is closed to perform the next molding operations. By repeating this operation, the shaft member of the finished piece is molded.

Although FIGS. 5A to 5C show a shaft member on which a total of three roller joint portions are molded, the number of roller joint portions can be arbitrarily changed, as a matter of course. To mold a shaft member having four roller joint portions, it suffices to arrange the fourth cavity for molding the fourth roller joint portion, in addition to the first to third cavities.

As described above, a shaft member having two roller joint portions may be molded by the first and second cavities.

The shaft member may be a shaft member on which one roller joint portion is molded by molding only a shaft portion by the first cavity and molding a roller joint portion by the second cavity.

FIGS. 6A to 6E show a mold according to another embodiment of the present invention. The mold according to the other embodiment is different from the first embodiment in the number of cavities for molding a shaft member and roller joint portion, and has a total of four cavities.

In FIG. 6A, the mold according to the present invention includes four different cavities.

In FIG. 6A, the mold includes a first cavity 26, a second cavity 27, a third cavity 28, and a fourth cavity 29. In the first cavity, only the shaft portion of a shaft member is molded, and no roller joint portion is molded. Roller joint portions are sequentially molded by the second to fourth cavities. Here, a mold having four cavities is described. However, the present invention is not limited to this, and the mold may have the first and second cavities or have the first, second, and third cavities.

FIG. 6B shows a state in which the mold is opened to eject an ejector plate after molding. The respective cavities include slides 30, and a plurality of inserts 31 which are arranged in the cavities 27 to 29 and have shapes each serving as a roller joint portion. An insert 32 for forming the shape of a molded article on the end face in the shaft direction is arranged at the end portion of each cavity on a side opposite to the slide 30 in the shaft direction.

Each slide 30 and each insert 32 incorporate center pins (not shown) which hold a shaft member serving as a molded article as the shaft center of each cavity. Simultaneously when the mold is opened, each slide 30 moves and is released from the molded article of a shaft member. Each insert 31 having the shape of a roller joint portion, and each insert 32 for forming the shape of a molded article on the end face in the shaft direction in each cavity move in the mold opening direction in conjunction with the operation of the ejector plate.

FIG. 6C shows a state in which molded articles (parts) molded by the respective cavities are released from the mold. A first part 261 is molded by a first cavity 26, a second part 271 is molded by the second cavity 27, a third part 281 is molded by the third cavity 28, and a fourth part 291 is molded by the fourth cavity 29.

In the embodiment, the molded articles (parts) molded by the respective cavities 26 to 29 move in a direction (direction perpendicular to the mold opening/closing direction) in which each slide 30 is set in the shaft direction. Then, the molded articles (parts) are released from the mold.

In the embodiment, the molded article 291 molded by the fourth cavity is a completed shaft member on which all roller joint portions are molded.

The mold having four cavities has been described above, but the present invention is not limited to this. When the mold has two, first and second cavities, the second part on which one roller joint portion is formed serves as a completed shaft member.

When the mold has the first, second, and third cavities, the third part on which two roller joint portions are formed serves as a completed shaft member.

FIG. 6D is a view showing a state in which the molded articles (parts) molded in FIG. 6C are inserted again in the mold. In FIG. 6D, the molded article (first part) 261 molded by the first cavity 26 is inserted in the second cavity 27, the molded article (second part) 271 molded by the second cavity 27 is inserted in the third cavity 28, and the molded article (third part) 281 molded by the third cavity 28 is inserted in the fourth cavity 29. At this time, nothing is inserted in the first cavity 26.

FIG. 6E shows a state in which the insertion of the molded articles (parts) is completed, and the inserted molded articles, slides 30, and inserts 31 move together with backward movement of the ejector plate. The mold is closed in the state of FIG. 6E to perform molding, thereby setting the state of FIG. 6A again.

As described above, roller joint portions can be sequentially formed by repeating the steps in FIGS. 6A to 6E, that is, inserting molded articles after molding sequentially in different cavities and molding them.

FIG. 7 is a perspective view showing a state in which molded articles are inserted in the cavities 26 to 29. A space 33 exists between each insert 31 for forming the shape of a roller joint portion, and the shaft portion of an inserted molded article (part). In molding, a resin is filled in the space 33 to mold a roller joint portion.

FIG. 8 is a perspective view showing another molded article of a shaft member molded by a mold and molding method according to each embodiment of the present invention.

The mold according to each of the above-described embodiments includes a maximum of four cavities. However, to mold a shaft member shown in FIG. 8, a mold incorporating nine cavities is prepared. First, a shaft member 60 and key groove 37 are molded by the first cavity, and rubber roller joint portions 35 and 36 which have different diameters and to which rollers are joined are molded sequentially by the second and subsequent cavities. Further, a gear 34 is molded by a gear piece which is arranged in the slide in the ninth cavity and has a gear shape.

Tables 1 to 4 show resin materials each used for the shaft member 10 molded using the mold 40 shown in FIG. 3, and the dimensions of finished pieces.

Related Art and Examples 1 to 4

Table 1 shows the results of molding using the mold (mold shown in FIG. 3) according to the present invention.

TABLE 1 Related Art Example 1 Example 2 Example 3 Example 4 Resin HIPS HIPS ABS PC PC + ABS Material Shaft φ8 φ8 φ8 φ8 φ8 Diameter (mm) Shaft Length 250 250 250 250 250 (mm) Diameter of φ10 φ10 φ10 φ10 φ10 Roller Joint Portion (mm) Number of 5 5 5 5 5 Roller Joint Portions Number of 1 6 6 6 6 Cavities Molding 50 25 25 25 25 Cycle (sec) Straightness 0.38 0.1 0.11 0.11 0.08 of Roller Shaft (mm) Circularity 58 24 19 25 22 of Roller (μm) Run-out of 0.3 0.06 0.06 0.05 0.05 Roller Portion (mm) PL Step of 0.05 0.05 0.05 0.05 0.05 Shaft Portion (μm) Step of 0.05 0 0 0 0 Roller Joint Portion (μm)

In Table 1, the related art represents the results obtained by molding the shapes of all the shaft member and roller joint portions by one cavity. Examples 1 to 4 represent the results of molding using the mold and molding method according to the present invention.

In the related art, since the portions of the shaft member and roller joint portions having different diameters were molded at once, the molding cycle became long, and a sink mark was generated at the roller joint portion, degrading the circularity. Further, since the parting line (PL) existed even at the roller joint portion, a parting step was generated at the roller joint portion.

To the contrary, in Examples 1 to 4 according to the present invention, only a φ8-mm shaft portion was molded by the first cavity, and φ10-mm roller joint portions were molded sequentially by the second and subsequent cavities. This was substantially the same as molding at a thickness of 2 mm.

For molded articles molded according to Examples 1 to 4, the molding cycle was greatly shortened. In addition, since no sink mark was generated at the roller joint portion, the circularity and run-out accuracy were improved. Further, since no parting line existed at the roller joint portion, no step was generated.

From Table 1, it was verified that a shaft member molded using the mold and molding method in each example of the present invention was superior in all productivity, part accuracy, and part function to the related art.

Examples 5 to 9

Table 2 shows the results of molding using the mold (mold shown in FIG. 3) according to the present invention.

TABLE 2 Example 5 Example 6 Example 7 Example 8 Example 9 Resin PC + GF50 PPO + PS + GF30 PBT + GF30 PPS + GF50 LCP + GF50 Material Shaft φ8 φ8 φ8 φ8 φ8 Diameter (mm) Shaft Length 250 250 250 250 250 (mm) Diameter of φ10 φ10 φ10 φ10 φ10 Roller Joint Portion (mm) Number of 5 5 5 5 5 Roller Joint Portions Number of 6 6 6 6 6 Cavities Molding 21 21 21 21 21 Cycle (sec) Straightness 0.07 0.05 0.08 0.1 0.1 of Roller Shaft (mm) Circularity 21 19 25 24 24 of Roller (μm) Run-out of 0.04 0.04 0.05 0.04 0.04 Roller Portion (mm) PL Step of 0.04 0.04 0.04 0.1 0.04 Shaft Portion (μm) Step of 0 0 0 0 0 Roller Joint Portion (μm)

In Table 2, the types of all resin materials are different in Examples 5 to 9. To increase the rigidity of the shaft member, a glass filler reinforcement is filled in all the resin materials.

As a result of molding each resin material by using the mold and molding method according to each example of the present invention, resin materials reinforced by various glass fillers improved the molding cycle and part accuracy, compared to glass fiber-free resin materials shown in Table 1.

Especially in Example 6, the same quality as that of a conventional part obtained by joining rollers to a metal shaft was achieved in all the straightness of the shaft member, the circularity of the roller joint portion, run-out of the roller portion, and the step of the roller joint portion.

Examples 10 to 14

Table 3 shows the results of foam molding using the mold (mold shown in FIG. 3) according to the present invention.

TABLE 3 Example 10 Example 11 Example 12 Example 13 Example 14 Resin HIPS ABS PC PC + ABS PC + GF50 Material Shaft φ8 φ8 φ8 φ8 φ8 Diameter (mm) Shaft Length 250 250 250 250 250 (mm) Diameter of φ10 φ10 φ10 φ10 φ10 Roller Joint Portion (mm) Number of 5 5 5 5 5 Roller Joint Portions Number of 6 6 6 6 6 Cavities Molding 21 21 21 21 21 Cycle (sec) Straightness 0.05 0.04 0.05 0.05 0.04 of Roller Shaft (mm) Circularity 18 15 17 18 17 of Roller (μm) Run-out of 0.04 0.03 0.04 0.04 0.03 Roller Portion (mm) PL Step of 0.05 0.05 0.05 0.05 0.04 Shaft Portion (μm) Step of 0 0 0 0 0 Roller Joint Portion (μm)

Table 3 represents the results obtained by mixing a foaming agent in various resin materials and performing foam molding by using the mold and molding method according to the present invention. As for the method of injecting and filling the foamed material, nitrogen gas is guided to the plasticating cylinder of an injection molding apparatus at high pressure and mixed with a resin in a high-temperature molten state in the cylinder, and the resultant mixture is injected into a mold to fill it.

In all the examples, the molding cycle and part accuracy were improved, compared to the results shown in Tables 1 and 2.

In all the examples, the same quality as that of a conventional part obtained by joining rollers to a metal shaft was achieved.

This result reveals that a conventional metal part could be replaced with a resin part, abruptly improving the productivity.

Examples 15 to 19

Table 4 shows the results obtained by integrally forming a gear shape on the end face shown in FIG. 8 by using the mold (mold shown in FIG. 3) according to the present invention.

TABLE 4 Example 15 Example 16 Example 17 Example 18 Example 19 Roller Shaft POM PBT + GF30 PC + GF50 PPS + GF50 LCP + GF50 Material Shaft φ8 φ8 φ8 φ8 φ8 Diameter (mm) Shaft Length 250 250 250 250 250 (mm) Gear POM POM POM POM POM Material Material of POM POM PC PPS LCP Roller Joint Portion Diameter of φ10 φ10 φ10 φ10 φ10 Roller Joint Portion (mm) Number of 7 7 7 7 7 Roller Joint Portions Number of 8 8 8 8 8 Cavities Molding 30 30 30 30 30 Cycle (sec) Straightness 0.12 0.04 0.04 0.07 0.06 of Roller Shaft (mm) Circularity 35 32 17 21 20 of Roller (μm) Run-out of 0.12 0.1 0.03 0.03 0.03 Roller Portion (mm) PL Step of 0.05 0.04 0.04 0.07 0.04 Shaft Portion (μm) Step of 0 0 0 0 0 Roller Joint Portion (μm)

In Table 4, each material is the result of foam molding, similar to Table 3.

In Example 16, a two-color molding apparatus was used. In Examples 17 to 19, in addition to the two-color molding apparatus, a compact injection unit was attached to a mold to perform three-color molding.

In all the examples in Table 4, the above-mentioned nitrogen gas was mixed in a resin to perform foam molding using only a plasticator configured to mold a shaft member.

In Example 15 in Table 4, all parts were molded using a POM material. Since the POM resin is higher in mold shrinkage factor than other resins, the accuracies of the shaft member and roller joint portion became poorer.

Example 16 exhibits the result of using resin materials among which only the material of the shaft portion was reinforced by a glass filler. Since the resin material reinforced by the glass filler was used for only the shaft portion, the accuracies of both the shaft portion and roller joint portion were improved, compared to Example 15.

In Examples 17 to 19, a resin material reinforced by a glass filler was used for the shaft portion, and the roller joint portion was molded using a resin material (unreinforced resin material) of the same type that was not reinforced by a glass filler.

In Examples 17 to 19, the accuracies of the shaft portion and roller joint portion substantially satisfied the standards.

In all Examples 15 to 19, the shape accuracy of the gear portion was almost the same and satisfied the standard.

Among the resin materials listed in Tables 1 to 4, HIPS stands for high-impact polystyrene, ABS stands for acrylonitrile butadiene styrene, and PC stands for polycarbonate. PPO stands for modified polyphenylene ether, PS stands for polystyrene, PBT stands for polybutylene terephthalate, PPS stands for polyphenylene sulfide, LCP stands for liquid crystal polymer, and POM stands for polyacetal. GF30 and GF50 indicate mixing ratios (%) of the glass filler, respectively.

Although the above-described examples used the glass filler as a filler for reinforcing a resin material, a carbon fiber, talc, or plate-like filler may be filled to reinforce a resin material. Also, a combination of these fillers can be used.

In the aforementioned examples, a roller joined to a shaft member was made of rubber. However, even a roller made of a substance other than rubber is also available.

In the mold for molding a resin shaft member according to the present invention, a plurality of parting-free insert can be arranged at portions to each of which a roller is press-fitted and joined. A plurality of cavities can be arranged in accordance with the number of roller joints.

Since a plurality of parting-free insert were arranged in the mold in accordance with the number of roller joint portions, the roller joint portions to each of which a roller was press-fitted and joined could be formed into a parting-free seamless shape.

In the present invention, therefore, the roller surface accuracy after press-fitting and joining, e.g., a rubber roller to a roller joint portion became high, and conventional roller surface polishing could be omitted.

A shaft requiring high rigidity was molded by the mold and molding method according to the present invention using a foamed material as the resin material. Hence, a cylindrical shaft member with high rigidity and high accuracy of a roller joint portion without any sink mark could be manufactured, and a metal shaft could be replaced with a resin shaft.

The resin shaft member according to the present invention could have high accuracy and high functionality at low cost, and could improve the productivity and quality.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2013-078494, filed Apr. 4, 2013, which is hereby incorporated by reference herein in its entirety. 

What is claimed is:
 1. A mold used to mold a resin shaft member including a shaft portion and a roller joint portion configured to join a roller, comprising a plurality of cavities of different shapes, wherein at least one of the plurality of cavities includes a space portion surrounded by a parting-free surface formed by an insert, and the insert is movable by an ejector in an opening/closing direction of the mold.
 2. The mold according to claim 1, wherein one of the plurality of cavities includes a gate configured to inject a resin into the space portion.
 3. The mold according to claim 1, wherein one of the plurality of cavities includes a gate configured to inject a resin into the shaft portion.
 4. A mold according to claim 1, wherein holding portions configured to support the shaft portion are formed at two end portions of the cavity, and one of the holding portions is movable in a direction perpendicular to the opening/closing direction of the mold.
 5. A method of manufacturing a resin shaft member including a shaft portion and a roller joint portion configured to join a roller, comprising: molding, by using a mold including at least a first cavity and a second cavity, a first part on which the shaft portion is molded by the first cavity, and molding a second part on which the roller joint portion is molded on the first part by the second cavity in which the first part is inserted.
 6. A method according to claim 5, wherein the roller joint portion is molded by injecting a resin into a space portion surrounded by a parting-free surface formed by an insert.
 7. A method according to claim 5, wherein the shaft portion and the roller joint portion are molded using a foaming resin.
 8. A method according to claim 5, wherein a diameter of the roller joint portion is larger that a diameter of the shaft portion.
 9. A method according to claim 5, wherein the first part and the second part are molded simultaneously.
 10. A method according to claim 5, wherein the mold further includes a third cavity, and a third molded article on which a second roller joint portion is molded at a position different from a position of the roller joint portion molded on the second molded article is molded by the third cavity in which the second molded article is inserted.
 11. A method according to claim 10, wherein the second roller joint portion is molded by injecting a resin into a space portion surrounded by a parting-free surface formed by an insert.
 12. A method according to claim 10, wherein the second roller joint portion is molded using a foaming resin.
 13. A roller shaft which is obtained by joining rollers to a plurality of roller joint portions of a resin shaft member on which a shaft portion and the plurality of roller joint portions are integrally molded, wherein the roller joint portion has a seamless shape.
 14. A shaft according to claim 13, wherein the roller shaft includes a gear portion on at least one end of the shaft portion.
 15. A shaft according to claim 13, wherein the shaft portion is molded from a resin material reinforced by one material selected from the group consisting of a glass filler, carbon fiber, talc, and plate-like filler, and the roller joint portion is molded from an unreinforced resin.
 16. A shaft according to claim 13, wherein the shaft portion includes a foam layer.
 17. A shaft according to claim 13, wherein the roller is formed from rubber. 